This application claims the priority of 196 17 561.5, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an adjustable telescopic steering column for motor vehicles and, more particularly, to a steering column having at least one longitudinally adjustable telescopic section which is held in an adjusted position by means of a locking device, and having a locking part which causes a holding force in the case of a crash which in a frictionally connected manner is applied to the adjustable telescopic section.
DE 29 04 205 C2 describes an adjustable telescopic steering column having an adjustable telescopic section held by a clamping device in a position which is determined as favorable as a result of a longitudinal and/or inclination adjustment. The clamping force required for this purpose is introduced by a swivellable operating lever which in a frictionally connected manner braces the legs of a bow surrounding the telescopic section in a U-shape with the walls of a vehicle-fixed holding part.
In the event of a crash of the vehicle with an impact by the occupant onto the steering wheel, a tilting movement of the known bow takes place and thus a tilting of the bow with the telescopic section, whereby an additional holding force is to be generated. This swivel movement of the bow requires, as a function of the force, a yielding deformation of the holding flanges of the bow on the walls of the holding part. The original clamping force between the bow and the holding part can no longer, however, be reliably obtained. The additional holding force becomes possible only with the impact by the occupant on the steering wheel.
DE 41 18 863 C1 discloses an adjustable telescopic steering column having an adjustable telescopic section held in different adjustable longitudinal and vertical positions by a clamping force introduced by an operating lever frictionally connected between console cheeks on both sides and a clamping body holding the telescopic section. In a vehicle crash, this clamping body is swivelled by the effect of a traction rope and is tilted with the adjustable telescopic section. Thereby, with the traction rope, the telescopic steering column can be pulled away from the occupant almost without any backlash. The clamping effect by the operating lever, by way of a clamping bolt on the console cheeks and the clamping body, is reduced by its swivelling.
EP 0 557 767 B1 describes an adjustable telescopic steering column for motor vehicles whose clamping force in the clamping device is intended to be improved in a crash by a certain alignment of the adjusting slot in the holding part.
DE 41 18 976 A1, DE 33 00 268 C2, EP 0 058 495 B1 and DE 83 00 261 U describe various adjustable telescopic steering columns which have a clamping locking system for the position-stable fixing of the telescopic sections on one another. This clamping locking system comprises vehicle-side and steering-column-side clamping legs which can be braced with respect to one another. As a result of the produced static friction, the telescopic sections are held on one another in an adjusted overlapping. When the vehicle is involved in a crash, this mechanical clamping device must be constructed with large clamping surfaces and a high bracing force. Otherwise, if its locking effect during the crash were discontinued because of the impacting occupant caused the steering wheel with its telescopic section to move in to the end stop, the driver would be stressed by high impact values in the case of the end stop.
Another approach for increasing the locking effect consists of constructing the clamping surfaces in a form-locking manner, as described in DE 36 19 125 C1 or DE 32 05 416 A1. A disadvantage in this approach, however, is a high-expenditure and difficult adjustability because the clamping surfaces are not completely detached from one another in order to maintain a certain adjusting resistance.
DE 33 39 926 C2 and DE 26 57 485 A1 describe safety steering columns having partial shafts which are fitted into one another. In the event of a crash, these shafts can be pushed further into one another, whereby a corrugated spring inserted between their walls is deformed in an energy-converting manner. A locking of the partial shafts to one another cannot be achieved by way of this corrugated spring. In addition, this energy-reducing process cannot be used in a telescopic steering column which permits a displacement of the partial shafts with respect to one another during the adjusting operation. A corresponding ball element which absorbs energy in a crash is also known from EP 0 629 540 A1.
An object of the present invention is to provide a telescopic steering column with an additional holding force for the adjustable telescopic section which acts early only in the case of a crash of the motor vehicle.
This object has been achieved in accordance with the present invention by constructing a locking part to act independently of the locking device for adjusting the position of the telescopic section.
The locking device for locking the adjustable telescopic section in the position desired for the occupant can be constructed here to be adapted to the vehicle with respect to the holding force and the operating comfort.
Only in the event of a crash, the independently acting locking part will be operated early, i.e. before the occupant impacts on the steering wheel, by way of the vehicle deceleration. As the result of its additional holding force, the locking part ensures the constant position of the longitudinally adjustable telescopic section. An influencing of the locking device for the adjusted position does not take place in this event.
Operation of the locking part by inertial force permits a simple and low-cost movement control. If useful, the locking part can also be changed into the operative position by a sensor-controlled adjusting device. A mechanical control of the acceleration-dependent operational point in time of the locking part can be implemented by a spring which keeps the locking part disengaged in a crash until the effect of the correspondingly high force takes place.
A bearing of the locking part on the position-stable telescopic section is advantageous for adjustability of the telescopic steering column because adjustment of its inclination will then have no influence on the necessary path of the locking part into the operative position in that the radial distance of the telescopic sections always remains the same.
The locking part can also be disposed independently of the telescopic steering column fixedly on the vehicle body, in which case additional possibilities exist for the arrangement of the locking part.
As a locking part, movable embodiments are suggested in the form of a wedge or a sheet metal strip, of a locking ball or a swivel cheek which can all be predetermined for an application case in a specific telescopic steering column construction.
The holding force of the locking part can also be adapted to the requirements recognized for a crash of the motor vehicle by a frictional application and/or a form-locking engagement on the adjustable telescopic section. Here, a deformation on the adjustable telescopic section, while reducing energy, may be additionally useful during the movement of the locking part into the operative position.
The movement of the locking part into the operative position can be transmitted by a toggle lever to another locking part which increasingly locks a movement of the adjustable telescopic section into the opposite direction or applies an additional holding force.